HEMOGLOBINOPATHIES - PowerPoint PPT Presentation

HEMOGLOBINOPATHIES. BIOCHEMISTRY DR AMINA TARIQ. A large number of mutations have been described in the globin genes. These mutations can be divided into two distinct types:

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Those that cause qualitative abnormalities (e.g. sickle cell anemia) and those that cause quantitative abnormalities (the thalassemias). Taken together these disorders are referred to as the hemoglobinopathies.

The mutation causing sickle cell anemia is a single nucleotide substitution (A to T) in the codon for amino acid 6. The change converts a glutamic acid codon (GAG) to a valinecodon (GTG). The form of hemoglobin in persons with sickle cell anemia is referred to as HbS.

Sickle cell anemia is an autosomal recessive disorder. This means that in order for full disease symptoms to manifest in an individual they must carry two copies (homozygous genotype = SS) of the HbS gene.

However, individuals who are heterozygous (genotype = AS) have what is referred to as sickle cell trait.

Thalassemia leads to damage to the internal organs, in particular the kidneys, heart and lungs. minor patients are heterozygous for β-thalassemia. Afflicted individuals harbor one normal β-globin gene and one that harbors a mutation leading to production of reduced or no β-globin.

Individuals that do not make any functional β-globin protein from 1 gene are termed β0heterozygotes. If β-globin production is reduced at one locus the individuals are termed β+heterozygotes. Thalassemia minor individuals are generally asymptomatic.

Mutations include : leads to damage to the internal organs, in particular the kidneys, heart and lungs.

1.Gene deletions

2.Point mutations in the promoter

3. Mutations in the coding region leading to defective initiation, insertions and deletions resulting in Frameshifts and Nonsense mutations

With the α-thalassemias the level of α-globin production can range from none to very nearly normal levels.

This is due in part to the fact that there are 2 identical α-globin genes on chromosome 16. Thus, the α-thalassemias involve inactivation of 1 to all 4 α-globin genes.

If hemoglobin level of 9 to 11g/dl. 3 of the 4 α-globingenes are functional, individuals are completely asymptomatic. This situation is identified as the "silent carrier" state or sometimes as α-thalassemia 2.

If 2 of the 4 genes are inactivated individuals are designated as "α-thalassemia trait"